Jim, K9YC, wrote: Speakers with built-in amplifiers are notorious for RFI. I often tour the aisles at audio trade shows with a THF6A VHF/UHF talkie. In ten years, I've seen only one amplified loudspeaker that didn't pick up RF. It cost about $1,500 and was made in Europe.
----------------------- Ha! Bet the vendors loved your "test" ;-) I've tried a couple of different "computer speakers" as well as conventional "bookshelf" audio system speakers on my K3 and have found no need for using an auxiliary amplifier. The K3 has plenty of audio power to drive external speakers in almost any Hamshack. I'm currently using a pair of LabTec "computer" speakers that bypass the internal amplifier by simply disconnecting the wall wart that supplies the amplifier. Ignacy, you might try that and see if they work without powering the internal amp. As Jim observes, the "ancient ones" (and most hams today) don't limit their audio response out of ignorance or because they couldn't. They knew that bass takes lots of power and generally interferes with intelligibility, especially in us guys. Not only do low frequencies hog power as Jim noted, they are hardly modulated when we produce speech. Our mouths and lips mostly modulate the higher harmonics, typically above 300 Hz. The fundamental tone and low-order power-hogging harmonics produced by our vocal cords are just a "drone" with little variation other than starting and stopping. Personally, I find that many modern SSB rigs do limit the high frequencies too much. For me, there's a big improvement in intelligibility between rolling off the highs quickly at 2.5 KHz and allowing a full 2.7 to 3.0 kHz through. 3.0 kHz was the "standard" communications upper frequency roll-off for many years going back through the AM days, and I find it's still preferable to me. A major difference today is that back "then" we simply rolled off the upper frequencies with the very simplest audio filtering - often just using bypass capacitors in the audio stages that tended to attenuate highs. The result was substantial audio energy being transmitted well above 3 kHz. Nowadays we have the filters to limit high frequencies much better. I understand that there's good evidence that, when digging for a signal in the noise, a lower upper-frequency limit can provide better communications (provided the lows below 300 Hz or so are also attenuated). It's a matter of concentrating the finite amount of RF into the most effective part of the audio spectrum. I find such "pinched" audio tiring to listen to for any amount of time, and losing the higher frequencies makes many phonemes harder to decode, perhaps because of the US Army's special gift to me (tinnitus from firing too many rounds from my M1 rifle parked next to my ear - our steel helmets don't come with ear protectors). Perhaps before long we'll start to see computer generated speech that is optimized for minimum bandwidth and maximum intelligibility rather than continue to use our clumsy, inefficient and highly variable biological speech mechanism called lungs, throat and mouth ;-) After all, we've largely dispensed with that personality in CW since most Hams have dumped their mechanical keys for keyers that compensate for most variations in fingers movements or even to a keyboard that eliminates any chance of human variability or inefficiency while "pounding brass". Ron AC7AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
